GoogleMap fragment inside fragment containing margin/padding at top?

Question

Using the "Activity Bottom Navigation" template in Android Studio, I am then adding a GoogleMap fragment inside one of the default fragments.

The main fragment, unchanged from the template:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0"
        app:navGraph="@navigation/mobile_navigation" />

The fragment that contains my mapfragment. Only slightly modified from the template's fragment:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.map.MapFragment">

    <fragment
        android:id="@+id/gmap"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    
</androidx.constraintlayout.widget.ConstraintLayout>

I am not including any code in the fragment, because it doesn't matter if there IS code or not - the margin/padding appears at top.

When run, I get the following:

Notice the almost-action-bar madding before the map starts. In the Android Studio designer screen, it IS shows that the fragment is taking up

Am I missing some kind of flag or setting or layout quirk to allow the map area to fill up the entire parent (its own) fragment?

Answer 1

The root ConstraintLayout on your main fragment is causing the empty space:

android:paddingTop="?attr/actionBarSize"

Delete this attribute and the space will disappear.